Heterometallic half-sandwich complexes containing a ferrocenyl motif: Synthesis, molecular structure, electrochemistry and antiplasmodial evaluation

The synthesis and characterisation of a series of new half-sandwich ruthenium(II), rhodium(III) and iridium(III) heterometallic complexes containing a ferrocenyl motif is reported. The dinuclear complexes were prepared by reaction of the ferrocenyl–salicylaldimine complex (1) with either [Ru(p-cymene)Cl2]2, [Rh(C5Me5)Cl2]2 or [Ir(C5Me5)Cl2]2 to yield heterobimetallic complexes where complex 1 acts as a bidentate anionic donor to ruthenium, rhodium or iridium via the imine nitrogen and phenolic oxygen atoms. The structures of the compounds have been confirmed using a variety of spectroscopic and analytical techniques, including single crystal X-ray diffraction analysis of complexes 2–4. The electrochemical behaviour of the heterometallic complexes was examined using cyclic voltammetry and a positive shift in the half-wave potential (E1/2) of the ferrocene/ferrocenium couple was observed for the Platinum Group Metal (PGM) complexes, indicating that the ferrocenyl moiety becomes harder to oxidise. The complexes were evaluated for antiplasmodial activity in vitro against the chloroquine-sensitive Plasmodium falciparum strain NF54, yielding IC50 values in the low micromolar range. Further analysis of complexes 1–4 using a β-hematin inhibition assay revealed that these complexes are able to inhibit the formation of synthetic hemozoin.